Project Summary The goal of this research is to elucidate fundamental mechanisms of biological self-organization, focusing on the rules that govern dynamics and organization of cellular actin structures. This question will be addressed using as a model system the polarized actin cables assembled in budding yeast. The proposal seeks to understand how 8-10 different conserved actin-regulatory proteins, each with a distinct functional role, work in concert to polymerize, stabilize, bundle, and dynamically turnover actin cables, endowing these structures with a characteristic length, architecture, and dynamics. The project combines in vitro reconstitution, genetics, live-cell imaging, multi-wavelength single molecule TIRF microscopy, structured illumination microscopy, and 4D confocal microscopy. The Aims are: (1) Use a novel in vitro actin cable reconstitution assay to dissect the mechanisms underlying cable assembly, turnover, and steady-state length control; and (2) Define the mechanisms controlling actin cable assembly, turnover, and architecture in vivo.